B. Protein Blotting

A general protocol for sample preparation.

Lyse cells by adding 1X SDS sample buffer (100 µl per well of 6-well plate or 500 µl for a 10 cm diameter plate). Immediately scrape the cells off the plate and transfer the extract to a microcentrifuge tube. Keep on ice.

Western Blot Reprobing Protocol

Reprobing of an existing membrane is a convenient means to immunoblot for multiple proteins independently when only a limited amount of sample is available. It should be noted that for the best possible results a fresh blot is always recommended. Reprobing can be a valuable method but with each reprobing of a blot there is potential for increased background signal. Additionally, it is recommended that you verify the removal of the first antibody complex prior to reprobing so that signal attributed to binding of the new antibody is not leftover signal from the first immunoblotting experiment. This can be done by re-exposing the blot to ECL reagents and making sure there is no signal prior to adding the next primary antibody.

(Optional) To assure that the original signal is removed, wash membrane twice for 5 min each with 10 ml of TBST. Incubate membrane with LumiGLO® with gentle agitation for 1 min at room temperature. Drain membrane of excess developing solution. Do not let dry. Wrap in plastic wrap and expose to x-ray film.

Wash membrane again four times for 5 min each in TBST.

The membrane is now ready to reuse. Start detection at the "Membrane Blocking and Antibody Incubations" step in the Western Immunoblotting Protocol.

Transfer 20 μl of bead slurry to a clean tube. Place the tube in a magnetic separation rack for 10-15 seconds.

Carefully remove the buffer once the solution is clear. Add 500 μl of 1X cell lysis buffer to the magnetic bead pellet, briefly vortex to wash the beads. Place tube back in magnetic separation rack. Remove buffer once solution is clear. Repeat washing step once more.

Add 200 μl cell lysate to 20 μl of pre-washed magnetic beads.

IMPORTANT: The optimal lysate concentration will depend on the expression level of the protein of interest. A starting concentration between 250 μg/ml-1.0 mg/ml is recommended.

Incubate with rotation for 20 minutes at room temperature.

Separate the beads from the lysate using a magnetic separation rack, transfer the pre-cleared lysate to a clean tube, and discard the magnetic bead pellet.

Species predicted to react based on 100% sequence homology:

Small non-coding RNAs are important regulators of gene expression in higher eukaryotes (1,2). Several classes of small RNAs, including short interfering RNAs (siRNAs) (3), microRNAs (miRNAs) (4), and Piwi-interacting RNAs (piRNAs) (5), have been identified. MicroRNAs are about 21 nucleotides in length and have been implicated in many cellular processes such as development, differentiation, and stress response (1,2). MicroRNAs regulate gene expression by modulating mRNA translation or stability (2). MicroRNAs function together with the protein components in the complexes called micro-ribonucleoproteins (miRNPs) (2). Among the most important components in these complexes are Argonaute proteins (1,2). There are four members in the mammalian Argonaute family and only Argonaute 2 (Ago2) possesses the Slicer endonuclease activity (1,2). Argonaute proteins participate in the various steps of microRNA-mediated gene silencing, such as repression of translation and mRNA turnover (1).